In the conventional commercial processes for the preparation of nylon 66 polymer, adipic acid and hexamethylene diamine are reacted. High molecular weight polymer is produced, but a by-product of this reaction is the formation of cyclic nylon 66 monomer, i.e. 1,8-diazacyclotetradecane-2,7-dione. 1,8-diazacyclotetradecane-2,7-dione has in the past been usually considered a waste product. It tends to be washed out of nylon fibers when the fibers are dyed.
1,8-diazacyclotetradecane-2,7-dione is disclosed in U.S. Pat. No. 2,241,323 to Greenewalt as a material suitable for use in the preparation of nylon polymers. In this patent the monomer is referred to as cyclic monomeric hexamethylene adipamide (14 annular atoms; M.P. 248 degrees C.)